Method of making transformer core



May 12, 1964 A. L. STOPPS 3,132,413

METHOD OF MAKING TRANSFORMER CORE Filed Jan. 27, 1961 FIGJ FKlfifi 12 36- 2o 2 Jav (Ff-WW FfiW F "F FIG? FIG.8

IO IO FIG. 9 FIGJO FIG.

INVENTOR ALFRED LESLIE STOPPS ATTORNEYS United States Patent Canada Filed Jan. 27, 1961, Ser. No. 35,243

4 Claims. (Cl. Zit -155.57)

This invention is a continuation-in-part of United States patent application, Serial No. 726,187, now abandoned, filed on the 3rd day of April 1958.

This invention relates to a method of forming a trans former core from three or more coils formed from a magnetic strip material and cut in staggered relation at right angles to an edge of the strip material to form them into individual loops. The coils so cut are reassembled in the same number of cores in which each loop occupies the same radial order as it did in itsrespective coil and in which the bridge to gap ratio is at least 4 to l.

The broad idea of reassembling loops taken from transversely cut coils into a transformer core is not new. For example, United States Patent No. 1,935,426, which issued on November 14, 1932, to H. M. Acly, shows a method of cutting a single coil and flipping and reassembling the loops so formed into a transformer core. Further, United States Patent No. 2,927,366, which issued on March 8, 1960, to E. A. Link, shows a manner of forming two coils and then cutting these coils and forming them into a single transformer core. Both of these methods differ basically from this invention in that this invention contemplates the forming of three or more coils cutting them in staggered relation at right angles to the axis of the strip from which they are formed and then reassembling the loops of the coils to form the same num-' ber of transformer cores.

In addition to the above noted two prior patents, there is a French Patent No. 1,111,097, issued to McGraw Electric Company, which teaches the reassembling of loops from two coils cut diagonally into two transformer cores. The diagonal cut recommended in this patent makes the reassembly of the loops more diflicult because they must be stressed to a greater extent as they are linked with a coil in use thereby risking flexing the steel beyond its yield point and adversely affecting its magnetic properties. Further, more iron is taken from the core by the out than with a right angled cut. This French patent goes to considerable length to show that a right angled cut is inferior to an inclined cut from the magnetic point of view in the case where two coils are formed from two coils. This inventor did not realize that by using the right angled cut and three or more coils he could achieve a core with a good gap to bridge ratio with good magnetic properties and thereby avoid the difliculties or" assembly and increased steel loss that results from the diagonal cut.

This invention and its advantages will be apparent after reading the following detailed specification read in conjunction with the drawings.

In the drawings,

FIGURE 1 refers to a wound coil formed with a cut to give a series of separate loops.

FIGURES 2 to 8 inclusive show the upper portions of wound coils similar to the coil illustrated in FIGURE 1 with the exception that the cut therein is offset.

FIGURE 9 is a view of a transformer core reassembled from loops from the coils of FIGURES 1-8 inclusive.

FIGURE 10 is a view along the line 10-40 of FIG- URE 9, and

FIGURE 11 shows a typical transformer assembly.

Referring to the drawings, the numeral 10 generally refers to a transformer core made according to this inven- 3,132,413 Patented May 12, 1964 2 tion. It is one of eight similar cores made by reassembling the loops of theeoils illustrated in FIGURES 1-8 inclusive.

Each of the coils shown in FIGURES 1-8 inclusive is wound on an arbour from magnetic strip material such as silicon steel and is similar to each of the other coils in dimension; The eight coils are generally referred to by numerals 12, 14, 16, 18, 20, 22, 24 and 26 respectively.

Coil 12 is cut as at 28 ina' plane that is substantially at right angles to the longitudinal edge of the magnetic strip material from which it is formed whereby to pro- 2 duce a plurality of individual loops radially arranged.

Coil 14 is similarly cut as at 30 but at a plane that is offset from the plane of cut 28 on the circumference of the coil.

In a similar way the remaining coils are cut but each cut is offset from each other cut. The cuts in the coils of FIGURES 3-8 inclusive are referred to by the numerals 32, 34, 36, 38, 40 and 42 respectively.

According to this invention the eight coils illustrated are cut to form loops as shown and reassembled into eight transformer cores, in which each loop occupies the same radial order as it did in its respective coil and in which adjacent loops are from different coils.

In the reassembly it will be noted that the eight loops taken in radial succession from the inside loop are from different coils. Thus, at any cross section where a gap occurs, the gap to bridge ratio is one to seven.

In the core shown in FIGURE 9 the loops of the eight coils have been intermingled but not flipped. If one were to make coils with double the number of turns to those shown in FIGURES 1-8 and to cut them in a similar way and intermingle the loops thereof to form a core, but in addition flip one-half of the loops before putting them in the core, one could achieve a gap to bridge ratio of one to fifteen. In such a case, the first eight loops of the core could be disposed as in FIGURE 9 and the next eight loops would be flipped through degrees so that the gaps therein would be on the opposite leg of the core. In such a case, it will be apparent that on a section such as the section 1li10 there would be a gap on the inside loop and the next fifteen loops would be solid metal. The practice of flipping is not the best practice in some cases. For example, with a typical assembly for a transformer as shown in FIG- URE 11, it is desirable that all of the gaps be within the core winding because it is much easier to assemble the core around the winding. Further, it is usually true that a better formed core results with more desirable electrical and magnetic qualities when flipping is not used.

However, it is within the scope of this invention to flip some of the turns to achieve a higher gap to bridge ratio.

It will benoted that the sequence of selecting the loops from the coils shown in FIGURE 9 is from coils 12, 20, 14, 22, 16, 24, 18, 26, and 12. The sequence is, of course, repeated if larger cores are used. In the drawings, the coils have been illustrated as having 9 loops. It will be appreciated that the number of loops could be increased.

After a core has been formed as illustrated in FIGURE 9, the steel may have been stressed during the winding, cutting and reassembling operation and I reanneal the core to restore its electrical properties. Following reannealing in the assembled form, the core is mounted on a coil illustrated by the numeral 44 as illustrated in FIG- URE 11. This is done by carefully taking the loops of the core apart and reassembling them on the coil 44, taking care not to stress the magnetic strip material beyond its yield point.

The gap to bridge ratio will depend upon the design of the transformer. Generally speaking, for most present areas-1s day design purposes a gap to bridge ratio of at least seven to one is desirable. This invention is concerned with the achievement of magnetic properties in such a core and the claims are limited to the case where the cores are formed from at least three separate coils cut in an offset manner at right angles to the axis of the strip so that they can be reassembled with a desirable gap. to bridge ratio, annealed and easily and conveniently embodied in a transformer assembly without danger of having to stress the individual loops beyond their yield point and thereby adversely affect the electrical properties. At the same time, the cut in the coils is atfected with a minimum of metal lost due to the cutting of the saw.

What I claim as my invention is:

.1. A method of making x laminated transformer cores comprising the steps of: winding x substantially identical coils each having opposed linear sides from magnetic strip material, x being a number greater than 2, cutting a single corresponding side of each of said x coils in a plane substantially at right angles to the longitudinal edges of the magnetic strip material from which they are made, whereby to produce a plurality of individual loops from each coil, each of said coils being cut as aforesaid offset along said single side from the cut in each of the other of said coils, reassembling the loops of said x coils intox transformer cores in which each loop occupies the same radial order as it did in its respective coil and in which adjacent loops are from different coils in sequences of x loops and the ends of the loops formed by cutting for each core are disposed along a common side of the core.

2. A method of making x laminated transformer cores as claimed in claim 1, in which said loops are reassembled as aforesaid and each loop of each coil occupies a different position in its core in each sequence at least to x sequences.

3. A method of making x laminated transformer cores as claimed in claim 1, wherein x is equal to any integer between 3 and 8 in which said loops define a gap at their free ends, said loops when reassembled into said cores defining a bridge at the cross sections of said-core where said gaps occur, the bridge to gap ratio being respectively 221, 3:1, 4:1, 5:1, 6:1, or 7:1 for the integers 3 through 8.

4. A method of making a laminated transformer core comprising the steps of winding x rectangularly shaped four sided substantially identical coils from magnetic strip material, x being a number greater than 2, cutting each of said x coils in a plane substantially at right angles to the longitudinal edges of the magnetic strip material from which they are made at a position across a corresponding side whereby to produce a plurality of individual loops from each coil, each of said coils being cut as aforesaid offset from the cut in each of the other of said coils, assembling from the loops of said x coils a transformer core in which adjacent loops of the respective cores are from ditferent coils in sequences of x loops and each loop of each. coil occupies a different position in its core, at least to x sequences.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF MAKING X LAMINATED TRANSFORMER CORES COMPRISING THE STEPS OF: WINDING X SUBSTANTIALLY IDENTICAL COILS EACH HAVING OPPOSED LINEAR SIDES FROM MAGNETIC STRIP MATERIAL, X BEING A NUMBER GREATER THAN 2, CUTTING A SINGLE CORRESPONDING SIDE OF EACH OF SAID X COILS IN A PLANE SUBSTANTIALLY AT RIGHT ANGLES TO THE LONGITUDINAL EDGES OF THE MAGNETIC STRIP MATERIAL FROM WHICH THEY ARE MADE, WHEREBY TO PRODUCE A PLURALITY OF INDIVIDUAL LOOPS FROM EACH COIL, EACH OF SAID COILS BEING CUT AS AFORESAID OFFSET ALONG SAID SINGLE SIDE FROM THE CUT IN EACH OF THE OTHER OF SAID COILS, REASSEMBLING THE LOOPS OF SAID X COILS INTO X TRANSFORMER CORES IN WHICH EACH LOOP OCCUPIES THE SAME RADIAL ORDER AS IT DID IN ITS RESPECTIVE COIL AND IN WHICH ADJACENT LOOPS ARE FROM DIFFERENT COILS IN SEQUENCES OF X LOOPS AND THE ENDS OF THE LOOPS FORMED BY CUTTING FOR EACH CORE ARE DISPOSED ALONG A COMMON SIDE OF THE CORE. 